Exhaust plenum for distributing exhaust gas uniformly through a catalyst module

ABSTRACT

A plenum is provided upstream from a catalyst module and downstream from a plurality of exhaust ports of a marine engine. The plenum is provided with a cross-sectional area that induces exhaust gas to slow as it passes from the plurality of exhaust ports into the plenum. This slowing of the velocity of exhaust gas improves the probability that the exhaust gas will be more evenly distributed across the inlet surface of the catalyst module.

CROSS REFERENCE TO CO-PENDING PATENT APPLICATION

This patent application is a member of a family of co-pending andcommonly owned patent applications which were all filed on ______, 2005.This family includes patent application (M09964) which was filed byWhite (Ser. No. ______), patent application (M09966) which was filed byWhite (Ser. No. ______), patent application (M09967) which was filed byBurk et al (Ser. No. ______), patent application (M09968) which wasfiled by White et al (Ser. No. ______), patent application (M09969)which was filed by White et al (Ser. No. ______), patent application(M09971) which was filed by White (Ser. No. ______), patent application(M09972) which was filed by White et al (Ser. No. ______), patentapplication (M09974) which was filed by White (Ser. No. ______), patentapplication (M09976) which was filed by White (Ser. No. ______).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally related to a catalyst module for amarine engine and, more particularly, to a system that provides a plenumupstream from the catalyst module to slow the velocity of exhaust gasfor the purpose of uniformly distributing the flow of exhaust gasthrough the inlet surface of the catalyst module.

2. Description of the Related Art

Those skilled in the art of internal combustion engines are aware ofmany types of catalyst systems that are available to improve exhaustemissions emitted by the engines.

U.S. Pat. No. 4,848,082, which issued to Takahashi et al. on Jul. 18,1989, describes an exhaust gas purifying device for a marine engine. Acatalyst exhaust system for an outboard motor is described. A throttlecontrol arrangement is incorporated for assuring rapid heating of thecatalyst to its operating temperature.

U.S. Pat. No. 4,900,282, which issued to Takahashi et al. on Feb. 13,1990, describes an exhaust gas purifying device for a marine engine. Acatalytic exhaust system for a marine outboard drive is describedwherein the catalyzer material is supported by a heat conductive bracketand the bracket is cooled by a cooling jacket that is supplied withcoolant from the engine cooling jacket. In one embodiment, the waterjacket is cooled both internally and externally by delivering water fromthe cooling jacket into the exhaust system to impinge upon a wall of thecooling jacket.

U.S. Pat. No. 5,133,185, which issued to Gilbreath et al. on Jul. 28,1992, describes an anti-moisture device for engine exhaust systems. Thedevice is intended to remove moisture droplets from an interior surfaceof a duct, characterized by an outer edge secured to the interiorsurface of the duct, an inner edge surrounding an opening, and aconnecting wall between the outer edge and the inner edge. The inneredge of the anti-moisture device is positioned closer to a downstreamend of the duct than the outer edge whereby the connecting wall ispositioned at an angle relative to the interior surface of the duct.Moisture droplets traveling upstream will be caught between theconnecting wall and the interior surface of the duct, on the downstreamside of the device.

U.S. Pat. No. 5,167,934, which issued to Wolf et al. on Dec. 1, 1992,describes a catalyzer installation for boat engines and a method forcatalytic exhaust gas cleaning. The invention is intended for use inboat engines and the catalyzer is subdivided into a reduction partlocation upstream in the exhaust gas line and an oxidation part locatedcoaxially downstream after it. An intermediate space is located betweenthe reduction and oxidation parts. Both catalyzer parts are surroundedby a preferably cylindrical, water cooled casing and the casing has adownstream secondary air inlet to which a secondary air blower can beconnected, the secondary air separating the very hot catalyzer from thedouble walled, water cooled casing and, in particular, flowing aroundthe oxidation catalyzer part in counterflow for air preheating so thatthe air preheating in this manner is passed through the intermediatespace into the oxidation part.

U.S. Pat. No. 5,203,167, which issued to Lassanske et al. on Apr. 20,1993, describes a marine propulsion device internal combustion engineand method for making the same. The propulsion device comprises adriveshaft housing, a propeller shaft rotatably supported by thedriveshaft housing, an internal combustion engine drivingly connected tothe propeller shaft, the engine including a cylinder block defining acylinder having an exhaust port, and defining an exhaust outlet, and anexhaust passage between the exhaust port and the exhaust outlet, anexhaust catalyst apparatus mounted on the cylinder block, the apparatusincluding a tongue extending into the cylinder block exhaust passage anddividing the cylinder block exhaust passage into an upstream portioncommunicating with the exhaust port and a downstream portioncommunicating with the exhaust outlet. The apparatus includes an exhaustpassage communicating between the upstream portion and the downstreamportion. The catalyst is located in the apparatus exhaust passage.

U.S. Pat. No. 5,212,949, which issued to Shiozawa on May 25, 1993,describes an exhaust gas cleaning system for a marine propulsion unit.It is intended for use with a watercraft engine. A plurality ofhorizontally positioned exhaust ports are located within an enginecylinder head. An exhaust manifold communicates with each of the exhaustports at a first end and forms a gas collecting pipe at its second end.The second end of the gas collecting pipe is positioned above theexhaust ports. A generally horizontally positioned exhaust pipe extendsfrom the second end of the gas collecting pipe and continues in arearward direction. Means are provided for introducing coolant from theengine into the rearwardly extending portion of the exhaust pipe.

U.S. Pat. No. 5,306,185, which issued to Lassanske et al. on Apr. 26,1994, describes catalytic elements for marine propulsion devices. Amarine propulsion device comprising a propulsion unit including apropeller shaft, a housing including an exhaust gas inlet and an exhaustgas outlet, a catalytic element supported in the housing forreorientation from a first orientation to a second orientation differentfrom the first orientation, and structure for reorienting the elementfrom the first orientation to the second orientation is described.

U.S. Pat. No. 5,324,217, which issued to Mineo on Jun. 28, 1994,describes an exhaust system for a small boat. It includes a water trapdevice for precluding water entering the exhaust system if thewatercraft becomes inverted from entering the engine through the exhaustsystem. Coolant from the engine is delivered to a cooling jacket thatencircles the entire exhaust system and is introduced into the exhaustgases downstream of the water trap so that in the event of inversion andrighting the engine coolant will also not enter the exhaust system. Thisalso provides protection for catalyzers in the exhaust system.

U.S. Pat. No. 5,408,827, which issued to Holtermann et al. on Apr. 25,1995, describes a marine propulsion device with improved catalystsupport arrangement. An internal combustion engine includes an exhaustport, an exhaust conduit communicating with the exhaust port and havingan inner surface, the conduit including first and second conduitportions having respective ends, the first and second conduit portionsbeing connected end to end, a catalyst which is located within theconduit and which includes catalytic material and a sleeve surroundingthe catalytic material, wherein the sleeve has a length and an outersurface spaced from the inner surface of the conduit along substantiallythe entire length of the sleeve. The sleeve has a rigid, radiallyoutwardly extending flange captured between the ends of the conduitportions, and a flexible gasket between the flange and the end of one ofthe conduit portions.

U.S. Pat. No. 5,425,232, which issued to Holtermann on Jun. 20, 1995,describes a marine propulsion device with means for supplying secondaryair to a catalytic converter. The marine propulsion device comprises acombustion chamber, an exhaust passage, an air pump and a three-waycatalytic converter. The air pump pumps air into the exhaust passage ator immediately upstream of the catalytic converter. By this constructionthe internal combustion engine can be run slightly rich, but thecatalytic converter will see a close to stoichiometric mixture so thatthe pollutants in the exhaust stream can be oxidized or reducedappropriately since the catalytic converter will be able to operate as athree-way catalytic converter.

U.S. Pat. No. 5,433,634, which issued to Nakayama et al. on Jul. 18,1995, describes an exhaust treatment for an outboard motor. The exhaustgases are normally discharged to the atmosphere at a point below thelevel of the body of water in which the watercraft is operating. Acatalyst bed is provided in the exhaust system and the catalyst bed isprotected from damage by pumping water from the exhaust conduit inresponse to certain conditions. These conditions may be either rapiddeceleration of the engine or watercraft, stopping of the engine, or anyof the combination of sensed factors. The water is pumped by a waterpump which is positioned either in the outboard drive or in the hull ofan associated watercraft. The pumping of water is initiated for only apredetermined time and until the sensed condition no longer is existent.

U.S. Pat. No. 6,053,785, which issued to Kato et al. on Apr. 25, 2000,describes an exhaust system and control for a marine propulsion engine.An outboard motor exhaust system and control for insuring good runningand effective exhaust gas silencing and treatment is provided. Thesystem includes a very compact exhaust system that includes an expansionchamber formed beneath the exhaust guide plate and to which the exhaustgases are delivered and removed at optimal locations. Furthermore, afeedback control employing a combustion condition sensor is employedalong with a catalyst in the exhaust. Sensors are provided upstream anddownstream of the catalyst to insure that it is operating at optimumconditions.

U.S. Pat. No. 6,116,022, which issued to Woodward on Sep. 12, 2000,describes a catalytic reactor for marine applications. The reactor foran internal combustion engine has a cooling jacket surrounding multiplecatalyst elements. A thermal barrier layer is formed between thecatalyst elements and the cooling jacket to prevent overcooling of thecatalyst elements. The thermal barrier layer can be formed frominsulating elements such as fibrous material, a plurality of annularrings disposed around the catalyst elements, a corrugated layer, or canbe formed by an empty space.

U.S. Pat. No. 6,368,726, which issued to Holpp et al. on Apr. 9, 2002,describes a honeycomb body configuration. It includes a honeycomb bodywith a fluid inlet side and a fluid outlet side. The honeycomb body isformed of at least partially structured sheet metal layers which formchannels through which a fluid can flow. The honeycomb body issurrounded by an inner tubular jacket and an outer tubular jacketprovided concentrically in relation thereto. The inner tubular jacket isconfigured as a corrugated hose in at least one axial subregion thereof.The inner tubular jacket has at least one further axis subregion whichlies smoothly against the honeycomb body. The corrugated subregion andthe outer tubular jacket are connected at least in a longitudinalpartial region of the corrugated subregion.

U.S. Pat. No. 6,639,193, which issued to Schaper on Oct. 28, 2003,describes a method and apparatus for end-surface connection of a carriermatrix of a honeycomb body by a joining technique. It relates inparticular to a catalyst carrier body. The matrix is disposed in atubular jacket and is laminated and/or wound from at least partiallystructured sheet metal foils or layers. The end surface of the honeycombbody is at least partially heated with the aid of a surface inductorhaving induction coils.

U.S. Pat. No. 6,660,235, which issued to Holpp et al. on Dec. 9, 2003,describes a catalyst carrier configuration for installation close to anengine. It includes a housing and at least one catalyst carrier bodydisposed in the housing. The catalyst carrier body has partition wallsdefining a plurality of passages for an exhaust gas. A flange surroundsthe catalyst carrier body and extends radially outwards from thecatalyst carrier body. The flange has a second that extends at leastpartially into an outer wall of the housing and can be disposed betweena cylinder head and a manifold of an internal combustion engine. Thecatalyst carrier configuration can be mounted close to an internalcombustion engine. A structural unit having at least two catalystcarrier configurations and an exhaust system are also provided.

U.S. Pat. No. 6,740,178, which issued to Kurth et al. on May 25, 2004,describes a method for producing a centered honeycomb body. The methodincludes forming a honeycomb body by stacking and/or winding layers ofsteel sheet containing chromium and aluminum resulting in the honeycombbody having channels through which a fluid can flow. The honeycomb bodyis introduced into a tubular jacket.

U.S. Pat. No. 6,799,422, which issued to Westerbeke et al. on Oct. 5,2004, describes an emission control method. It is intended for use witha fixed speed internal combustion engine and includes injecting acontrolled flow of air into the exhaust between a first catalyst bedadapted to reduce hydrocarbon and nitrogen oxide emissions and a secondcatalyst bed adapted to reduce carbon monoxide emissions.

The patents described above are hereby expressly incorporated byreference in the description of the present invention.

SUMMARY OF THE INVENTION

An exhaust system for a marine engine made in accordance with apreferred embodiment of the present invention, comprises a plurality ofexhaust ports associated with a plurality of cylinders of the marineengine, a catalyst module disposed in fluid communication with theplurality of exhaust ports and a plenum disposed in fluid communicationbetween the plurality of exhaust ports and the catalyst module. Exhaustgas passing from the plurality of exhaust ports to the catalyst modulepass through the plenum. The catalyst module is disposed in series withthe plenum and the plurality of exhaust ports are disposed in parallelwith each other and in series with the plenum. The catalyst module cancomprise catalyst coded material disposed within a generally cylindricalhousing. The housing is configured to conduct the exhaust gas throughthe generally cylindrical housing in a direction which is parallel to acentral axis of the housing and in contact with the catalyst codedmaterial. The central axis is generally vertical and an unobstructedpath exists through the plenum to the catalyst module. The effect ofcross-sectional area of the plenum, at a plane midway between theplurality of exhaust ports and the catalyst module and generallyperpendicular to the path of the exhaust gas, is greater than the effectof total cross-sectional area of the plurality of exhaust ports. Theplenum is configured to cause the velocity of the exhaust gas todecrease as it passes from the plurality of exhaust ports into theplenum.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully and completely understood froma reading of the description of the preferred embodiment in conjunctionwith the drawings, in which:

FIG. 1 is a side view of a marine engine which is partially sectioned toshow internal portions of the exhaust system;

FIG. 2 is an isometric partially sectioned view of the port andstarboard exhaust components;

FIG. 3 is a section view of the port exhaust system of a marine engine;

FIG. 4 is a partially sectioned isometric view of the device shown inFIG. 3;

FIG. 5 is an exploded isometric view of the port side exhaust system ofthe present invention;

FIG. 6 is a section view of the port side exhaust system of a marineengine; and

FIG. 7 is an alternative exhaust system using an oblong catalyst device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Throughout the description of the preferred embodiment of the presentinvention, like components will be identified by like referencenumerals. In the following description of various embodiments of thepresent invention, certain configurations will be described andillustrated as having three catalyst devices used together as a system.It should be clearly understood that the catalyst devices canalternatively be combined together in systems comprising less than orgreater than this number. In addition, it should also be clearlyunderstood that certain embodiments of the present invention cancomprise a single catalyst device. All of these alternativeconfigurations are described below in relation to an exemplary enginearrangement. In addition, it should be understood that a catalyst systemmade in accordance with a preferred embodiment of the present invention,when used in conjunction with a V-type engine, would typically beprovided at both sides, or cylinder banks, of the engine.

FIG. 1 shows a marine engine 10 within the structure of a marine vessel12. Although not shown in FIG. 1, the crankshaft of the engine 10 issupported for rotation about a horizontal axis and attached in torquetransmitting relation with a driveshaft that extends through the transom14 to provide motive power to a marine propulsion drive (not shown inFIG. 1). The marine engine 10 has a plurality of exhaust ports 20configured to conduct exhaust gas from a plurality of cylinders withinthe structure of the engine. A first exhaust conduit 22 is disposed influid communication with the plurality of exhaust ports 20. The firstexhaust conduit 22 performs the function of an exhaust manifold whichreceives the exhaust gas from the plurality of exhaust ports 20 anddirects it away from the engine 10. A plurality of catalyst devices23-25 is disposed in fluid communication with the first exhaust conduit22. The plurality of exhaust conduits, as will be described in greaterdetail below, are configured and arranged in cooperation with the firstexhaust conduit 22 to assure that all of the exhaust gas passes throughthe plurality of catalyst devices 23-25. A second exhaust conduit 28 isdisposed in fluid communication with the plurality of catalyst devices23-25. The catalyst devices are disposed in serial fluid communicationbetween the first and second exhaust conduits, 22 and 28. Each one ofthe plurality of catalyst devices 23-25 is disposed in parallel fluidcommunication with each other.

With continued reference to FIG. 1, the first exhaust conduit 22, orexhaust manifold, is disposed in serial fluid communication between theplurality of exhaust ports 20 and the plurality of catalyst devices23-25. The second exhaust conduit 28 is disposed in serial fluidcommunication with the plurality of catalyst devices 23-25. The catalystdevices 23-25 are aligned along a common plane. The common plane isgenerally vertical and extends in a direction which is generallyparallel with a crankshaft of the engine 10.

Each of the catalyst devices 23-25, in a particularly preferredembodiment of the present invention, comprises a cylindrical housing.The housing can alternatively be generally tubular and non-cylindrical.A catalyst material is disposed within the generally tubular housingstructure of each of the catalyst devices 23-25. A central housing 30,or catalyst housing structure, is provided to retain the catalystdevices 23-25 in their proper positions relative to both the first andsecond exhaust conduits, 22 and 28. The path of the exhaust gas E isrepresented by the arrows in FIG. 1. The exhaust gas travels from theplurality of exhaust ports 20, through the first exhaust conduit 22,through the catalyst devices 23-25, and through the second exhaustconduit 28. From there, as is generally understood by those skilled inthe art, the exhaust gas is directed away from the engine 10 eitherthrough the transom 14 and to an underwater outlet or through exhaustpipes above and to the rear of the engine 10.

With continued reference to FIG. 1, it should be understood that one ofthe advantages of a preferred embodiment of the present invention isthat the use of three catalyst devices 23-25 reduces the overallrequired size of the components associated with the exhaust system. Inother words, three catalyst devices 23-25 of a lesser diameter can bealigned as shown in FIG. 1 in a space that requires less overall widthof the engine structure than would be needed if a single circularcatalyst device was used. It should be understood that, when the marineengine 10 is a V-type engine, two exhaust systems are provided, one onthe port side of the engine as shown in FIG. 1 and a similarlyconfigured exhaust system on the starboard side of the engine.

FIG. 2 is an isometric and partially sectioned view of two exhauststructures used in conjunction with one embodiment of the presentinvention. A port exhaust structure 40 and a starboard exhaust structure42 are shown in FIG. 2. The port exhaust structure 40 is sectioned toillustrate various internal characteristics. The exhaust manifold, orfirst exhaust conduit 22, directs the exhaust gas E from exhaust portsof the engine, as described above, through a plenum region 44. Thecentral housing structure 30, or catalyst housing structure, has aplurality of generally tubular cavities 43-45 formed therein. Each ofthe tubular cavities is shaped to receive one of the catalyst devices23-25 which are described above in conjunction with FIG. 1. Thosecatalyst devices are not shown in FIG. 2. Each of the tubular cavities43-45 is sized to define a space between an inner surface, such assurfaces 47-49, of the cavities 43-45, respectively, and an outersurface of the generally tubular structure of the catalyst devices23-25. This generally annular space thus defined by the sizes of thecatalyst devices 23-25 and the generally tubular cavities 43-45 providesan important thermally insulative function between the catalyst devicesand the catalyst housing structure 30. As shown in FIG. 2, coolingpassages 50 are provided to limit the temperature of the first exhaustconduit 22, the catalyst housing structure 30, and the second exhaustconduit 28. However, many types of catalyst devices operate moreefficiently and effectively at raised temperatures. Therefore, it canbecome counterproductive if the catalyst devices 23-25 receive a coolingeffect as a result of the water passing through the cooling passages 50.

By providing a space between the catalyst devices 23-25 and thererespective tubular cavities 43-45, this cooling effect is reduced. As aresult of this insulating space, the catalyst devices 23-25 operate athigher temperatures because of the temperature of the exhaust gas Epassing through them.

FIG. 3 is a sectioned view of the port exhaust device 40. Withparticular reference to catalyst device 23 in FIG. 3, it can be seenthat the outer surface 54 of the generally tubular member 56 is smallerthan the inner surface 60 of the associated tubular cavity which isdescribed above in conjunction with FIG. 2 and identified by referencenumeral 43. This difference in size between the outer surface 54 and theinner surface 60 defines the generally annular space 70 surrounding thecatalyst device 23. As a result, heat is not efficiently communicatedaway from the catalyst device 23 toward the inner surface 60 of thetubular cavity which is cooled by the water passages 50. The catalystdevices 23-25 therefore operate at higher temperatures than would bepossible if their tubular structures were in direct thermal contact withthe inner walls of their associated tubular cavities.

FIG. 4 is a partially sectioned view of the port exhaust device 40. Theview of FIG. 4 is a section taken along a plane that is generallyhorizontal and intersects the catalyst housing structure 30 and thethree catalyst devices 23-25. This plane of intersection is illustratedin FIG. 3 and identified by dashed line 66.

In FIG. 4, the space between the outer surface 54 of the tubularcatalyst device and the inner cylindrical surface 60 of the tubularcavity is identified by reference numeral 70. This space is generallyannular and circular in cross-section except in the region directlybetween adjacent catalyst devices 23-25. In that region the space,identified by reference numeral 72, is larger because of the geometry ofthe components and the fact that adjacent tubular cavities, identifiedby reference numerals 43-45 in FIG. 2, are not isolated from each other.Also shown in FIG. 4 is a water jacket 50 surrounding the wall 76 thatdefines the generally tubular cavities 43-45.

FIG. 5 is an isometric view of the port exhaust device 40 with thecatalyst housing structure 30 separated to expose the three catalystdevices 23-25. The exploded view of FIG. 5 also shows the catalystdevices 23-25 spaced apart from the first exhaust conduit 22 or exhaustmanifold. Several characteristics of the preferred embodiment of thepresent invention can be seen in the exploded isometric view of FIG. 5.Each of the catalyst devices 23-25 has a tubular portion, which isgenerally cylindrical in the embodiment shown in FIG. 5, and a rim 80which is configured to lie in a plane which is generally perpendicularto a central axis of the tubular portion of the catalyst device. Theserims 80 are configured to support the associated catalyst device on anupper surface 84 of the first exhaust conduit 22, or exhaust manifold.In other words, the outer diameter of the rim 80 is greater than theinner diameter 86 of an associated opening formed in the upper surface84 of the exhaust manifold or first exhaust conduit 22. These relativesizes of the openings 86 and rims 80 prevent the catalyst devices 23-25from passing into the associated opening 86. When the catalyst housingstructure 30 is attached to the exhaust manifold 22, the rims 80 of thecatalyst devices 23-25 are captured between opposed flange surfaces.Under the rims 80 is the surface identified reference numeral 84 andabove the rims 80 is the lower surface of the catalyst housing structure30. As a result of the space 70 described above in conjunction with FIG.4, the catalyst devices 23-25 are generally in non-contact associationwith the catalyst housing structure 30. They are supported by theirrelationship of the rims 80 with the upper surface 84 of the firstexhaust conduit 22 and a lower surface of the catalyst housing structure30.

With continued reference to FIG. 5, a gasket 90 is disposed on theflange surface 84 of the first exhaust conduit 22. It has a centralopening 92 formed therethrough. The central opening 92 formed throughthe gasket 90 is sized to allow the rims 80 to rest on the surface 84within the size of the opening 92. In other words, when the catalysthousing structure 30 is attached to the exhaust manifold 22, the rims 80are in contact with surface 84 and the lower surface of the catalysthousing structure 30, but the gasket 90 is not disposed between the rims80 and either surface.

With reference to FIGS. 3 and 5, it can be seen that the rims 80 providea seal at the bottom of the spaces identified by reference numerals 70and 72 and described above in conjunction with FIG. 4. This seal at thebottom of these spaces inhibits a liquid, such as water, from flowingdownward out of the spaces 70 and 72. As such, the seal cooperates withthe space to form a reservoir that captures water which may flow alongthe walls of the catalyst housing structure 30 under the effect ofgravity. This water can result from condensation formed on the innerwalls of the catalyst housing structure 30. If that condensation occurs,the seal provided by the rims 80 at the bottom portions of the catalystdevices 23-25 inhibits the flow of that water into the exhaust manifold22 and, eventually, into the exhaust ports of the engine. When thecatalyst devices 23-25 reach elevated temperatures, as a result of theirdirect exposure to the exhaust gas E, the increased temperature willboil the captured water within the reservoir of the spaces 70 and 72 andthat resulting water vapor will pass upwardly through the catalysthousing structure 30 and out of the second exhaust conduit 28 with theexhaust gas.

FIG. 6 is a section view of the exhaust manifold 22, or first exhaustconduit, and the catalyst housing structure 30 attached to it. FIG. 6also shows the surface 100 of the exhaust manifold which can be rigidlyattached to a surface of the engine through which exhaust gas isconducted through its exhaust ports. Reference numeral 102 identifies agasket between surface 100 of the exhaust manifold 22 and thecorresponding surface of the engine surrounding the exhaust ports. Theexhaust gas E flows from the exhaust ports of the engine, through theexhaust manifold 22 and through the catalyst devices 23-25 as describedabove in conjunction with FIGS. 1-5. The space 70 is shown in FIG. 6surrounding the outer surface 54 of the generally tubular portion of thecatalyst device and the inner surface 60 of the generally tubular cavityformed within the catalyst housing structure 30.

Throughout the description of the exhaust system with reference to FIGS.1-6, the catalyst devices 23-25 have been illustrated and described asbeing generally cylindrical in cross-section. However, it should beunderstood that this generally cylindrical shape is not necessary in allembodiments of the present invention. As an example, an oblong-shapedcatalyst device can also be used. FIG. 7 shows an oblong-shaped catalystdevice 123 disposed within a catalyst housing structure 130. The oblongnature of the catalyst device can be seen from its major axis 132 andthe arrow 134 which represents half of its minor axis illustrated in thesection view of the catalyst device 123 in FIG. 7. The structure shownin FIG. 7 directs exhaust gas through four pipes 141-144 which conductthe exhaust gas to a plenum region 144 where the exhaust gas from eachpipe is free to combine with gas from other pipes within the plenum 144of the catalyst housing structure 130. The exhaust gas passes throughthe plenum 144 and then through the catalyst device 123. After flowingthrough the catalyst device 123, the exhaust gas E flows into andthrough the second exhaust conduit 28.

The exhaust system described above in conjunction with FIGS. 1-7exhibits numerous advantageous characteristics which improve theoperation of a marine engine. These characteristics will be described ingreater detail below in conjunction with the specific figures that bestillustrate those characteristics.

FIG. 7 illustrates the oblong catalyst device 123 and FIG. 1 shows therelative positions of the exhaust ports 20 on the marine engine 10. Itshould be understood that the generally cylindrical exhaust devices23-25 could be replaced within the catalyst housing structure 30 by anappropriately shaped oblong catalyst device such as that which isidentified by reference numeral 123 in FIG. 7.

With reference to FIGS. 1 and 7, one embodiment of the present inventioncomprises a plurality of exhaust ports 20, a first exhaust conduit, 22or 122, an oblong catalyst device 123 and a second exhaust conduit, 28or 128. The first exhaust conduit 122 is disposed in fluid communicationwith the plurality of exhaust ports by the exhaust pipes 141-144. Theoblong catalyst device 123 is disposed in fluid communication with thefirst exhaust conduit, 22 or 122. The oblong catalyst 123 has a majoraxis 132, a minor axis, half of which is represented by arrow 134, and acentral axis which extends through the catalyst device in a directiongenerally parallel to the arrows representing the flow of exhaust gas E.The oblong catalyst device is configured to conduct the exhaust gas E ina direction generally perpendicular to the major and minor axes, 132 and134, and generally parallel to the central axis. The second exhaustconduit, 28 or 128, is disposed in fluid communication with the oblongcatalyst device 123. The oblong catalyst device is disposed in serialfluid communication between the first and second exhaust conduits, 122and 128.

The configuration of a preferred embodiment of the present invention,described above in conjunction with FIGS. 1-7, promotes a generallyuniform flow of exhaust gas through the catalyst module, whether thecatalyst module comprises a plurality of catalyst devices 23-25 orwhether it comprises a single larger catalyst device 123. With referenceto FIGS. 2 and 6, the exhaust gas E flowing into the exhaust manifold22, or first exhaust conduit, flows from regions of relatively smallercross-sectional area (e.g. the exhaust ports of the engine) to a plenumarea 44 having a greater cross-sectional area. As a result of thisincrease in cross-sectional area along the path of the exhaust gas E,the velocity of the exhaust gas decreases. This allows the exhaust tomore uniformly seek areas of lower pressure along the inlet surfaces ofthe catalyst devices 23-25. In other words, without the plenum area 44,the exhaust gas stream would be more subject to the influences of gasstream velocity and momentum that could urge the exhaust to flow throughlimited portions of the inlet area of the catalyst devices. However,when a plenum 44 is provided, the velocity of the gas stream slows andallows the exhaust to more uniformly seek lower pressure areas along theinlet surfaces of the catalyst devices. Rather than directing theexhaust gas stream with a restrictive conduit, the expanded area 44 ofthe plenum decreases the velocity of the flow and encourages a moreuniform distribution of the exhaust gas through the plurality of exhaustdevices or, alternatively, through all of the areas of the inlet of asingle catalyst device.

With reference to FIGS. 1 and 3, a non-catalytic porous member 150 isdisposed within the second exhaust conduit 128. This non-catalyst porousmember can be made of the same material used to begin the manufacturingprocess associated with the catalyst devices 23-25. That manufacturingprocess is described in U.S. Pat. Nos. 6,368,726 and 6,639,193. U.S.Pat. Nos. 6,660,235 and 6,740,178 also describe the manufacturingprocess associated with creating a catalyst device. The internalportions of the catalyst devices described in those patents comprise asupport structure which is porous. The support structure is alsoprovided with a catalytic material to manufacture a catalyst device. Thenon-catalytic porous member 150 comprises the internal supportstructure, but without the catalytic material being included. Itspurpose is not to serve as a catalyst device. Its purpose is to serve asa structure which inhibits the flow of liquid water in a reversedirection through the second exhaust conduit 28. Exhaust gas freelypasses through the porous non-catalytic member as it flows away from theengine 10. As a result, the non-catalytic porous member is heated toapproximately the temperature of the exhaust gas stream. If waterattempts to migrate in a reverse direction through the non-catalyticporous member 150, it will be rapidly evaporated and the resulting vaporwill be carried away from the engine 10 by the exhaust stream. Thisembodiment of the present invention provides an exhaust conduit 128disposed in serial fluid communication downstream from a plurality ofexhaust ports 20 as described above. The non-catalytic porous member cancomprise a metallic mesh material and it can be configured to direct theexhaust gas through the metallic mesh material. In a preferredembodiment, the non-catalyst porous member comprises a metalliccatalytic substrate, but without a catalytic coating.

The embodiment of the present invention described above in conjunctionwith FIGS. 1-6 comprises a catalyst device (e.g. devices 23-25) thatcomprises a first catalyst material disposed within a first housingstructure, such as the tubular or cylindrical structure illustrated inFIG. 5. The tubular portion of the catalyst devices has a central axis.The rim portion 80 extends from an end of the generally tubular portionand is disposed in a plane which is generally perpendicular to thecentral axis of the tubular portion. A gasket 90 is disposable betweenthe exhaust manifold 22 and the catalyst housing structure 30. Thegasket 90 is disposed between the two flange surfaces which include theupper surface 84 of the exhaust manifold 22 and the lower surface of thecatalyst housing structure 30. The gasket has an opening 92 which isformed through its thickness. The opening 92 is configured to receivethe rim portion 80 of a catalyst device. The size of the opening 92 isselected to allow the rim portions 80 to be captured between the uppersurface 84 of the exhaust manifold 22 and the lower surface of thecatalyst housing 30 without the gasket 90 being compressed between therim portion 80 and either of the two flange surfaces.

As described above in conjunction with FIGS. 3, 4 and 6, the outersurface 54 of each tubular catalyst device 23-25 is shaped to bereceived within an associated tubular cavity 43-45 with a space 70therebetween. The space 70 is a generally annular space defined by thedifference in size between the outer surface 54 of the catalyst devices23-25 and the inner surface 60 of the associated tubular cavity. Thisspace 70 provides an effective thermal insulation between the catalystdevices 23-25 and the catalyst housing structure 30. The presence of therim 80 at the bottom portion of each catalyst device 23-25 provides aseal which prevents liquid from flowing downward and out of the space 70if liquid is trapped therein. As a result, a reservoir is defined whichholds the liquid until the temperature becomes sufficiently high to boilthe liquid and allow the water vapor to escape with the gas stream.

With reference to FIG. 5, a concentricity spacer 160 is provided foreach of the catalyst devices 23-25. The purpose of the concentricityspacer is to maintain the outer cylindrical surface of the catalystdevices in a concentric relationship with the inner cylindrical surfaceof the associated tubular cavity 43-45. The concentricity spacer 160, ina preferred embodiment of the present invention, comprises a relativelythin sheet of material that is embossed with raised portions whichmaintain the concentricity of the catalyst device and its associatedtubular cavity while allowing fluid to flow in a vertical direction pastthe concentricity spacer.

With reference to FIGS. 3 and 4, two oxygen sensors are illustrated. Anupstream oxygen sensor 170 is disposed in fluid communication with theexhaust gas passing through the exhaust manifold 22. A downstream oxygensensor 175 is disposed in the upper portion of the catalyst housingstructure 30.

As shown in FIG. 4, the upstream oxygen sensor 170 is disposed withinthe overall exhaust structure and, more specifically, within the exhaustmanifold 22. It is therefore disposed downstream from the plurality ofexhaust ports 20 (shown in FIG. 1) and upstream from the catalystdevices 23-25. The oxygen sensor 170 is configured to remain at or belowthe temperature of the exhaust gas E when the exhaust gas is flowingfrom the plurality of exhaust ports 20 as shown in FIG. 1. In otherwords, the oxygen sensor 170 located upstream from the catalyst devices23-25 is unheated other than the effect it experiences from the hotexhaust gas flowing over it. The unheated nature of the upstream oxygensensor 170 provides a significant advantage because it is lesssusceptible to damage in the event that liquid, such as watercondensate, flows in a reverse direction from the second exhaust conduit28 toward the plurality of exhaust ports of the engine 10. If theupstream oxygen sensor 170 is heated, as most oxygen sensors now are, itcould be severely damaged if water flows in contact with it. The use ofan unheated oxygen sensor 170 therefore provides a significant benefitin an exhaust system of a marine engine.

FIG. 3 illustrates an advantage provided by the system described hereinin conjunction with a reverse flow of liquid, as represented by arrowsW, from the second exhaust conduit 28 toward the catalyst devices 23-25.The downstream oxygen sensor 175 is disposed within the catalyst housingstructure 30 and in fluid communication with the plurality of exhaustports 20 described above in conjunction with FIG. 1. It is also disposedin fluid communication with the second exhaust conduit 28. The secondexhaust conduit 28 is connected to a first portion of the catalysthousing structure 30 which, as illustrated in FIG. 3, is at the upperright portion of this device. The oxygen sensor 175 is connected to asecond portion of the catalyst housing structure 30 which is located atthe upper left portion as shown in FIG. 3. In a preferred embodiment ofthe present invention, the first and second portions are disposed atopposite sides of the catalyst housing structure 30 as shown.

With continued reference to FIG. 3, the first exhaust conduit 22, thecatalyst housing structure 30 and the catalyst device 23-25 areconfigured and arranged to cooperatively define a reversion liquidtrajectory path W for water that flows in a direction from the secondexhaust conduit 28 toward the first exhaust conduit 22. This reversionliquid trajectory path is governed by the positions of the secondexhaust conduit 28 and the catalyst devices 23-25 in conjunction withthe resulting inertia of the water droplets as they flow under theeffect of differential pressure that can result from the opening ofexhaust valves of the engine.

The causes for water reversion are well known to those skilled in theart of marine propulsion systems. As water droplets are caused to flowin a reverse direction, as indicated by arrows W, the trajectory ofthose water droplets is governed by the magnitude of the differentialpressure between the second exhaust conduit 28 and the first exhaustconduit 22 in conjunction with the size of the various droplets, theshape of the internal cavity of the catalyst housing structure 30, andthe positions of the upper portions of the catalyst devices 23-25. Thelocation of the downstream oxygen sensor 175 is selected, in a preferredembodiment of the present invention, to be away from this reversionliquid trajectory path illustrated by arrows W in FIG. 3. As such, thewater droplets are less likely to strike the downstream oxygen sensor175. This advantageous location of the downstream oxygen sensor 175therefore avoids damage that would otherwise occur to it if the hotsensor 175 is struck by water droplets flowing in a reverse directionfrom the second exhaust conduit 28 toward the catalyst devices 23-25.

Although the present invention has been described in particular detailand illustrated to show various embodiments, it should be understoodthat alternative embodiments are also within its scope.

1. An exhaust system for a marine engine, comprising: a plurality ofexhaust ports associated with a plurality of cylinders of said marineengine; a catalyst module disposed in fluid communication with saidplurality of exhaust ports; and a plenum disposed in fluid communicationbetween said plurality of exhaust ports and said catalyst module,wherein exhaust gas passing from said plurality of exhaust ports to saidcatalyst module must pass through said plenum, wherein the effectivecross sectional area of said plenum monotonic ally decreases from saidplurality of exhaust ports to said catalyst module.
 2. The exhaustsystem of claim 1, wherein: said cross sectional area of said plenumdecreases along the entire span of exhaust flow from said plurality ofexhaust ports to said catalyst module without changing to increasingvalues of said cross sectional area.
 3. The exhaust system of claim 1,wherein: said plurality of exhaust ports are disposed in parallel witheach other and in series with said plenum.
 4. The exhaust system ofclaim 1, wherein: said catalyst module comprises catalyst coatedmaterial disposed within a generally cylinder housing, said generallycylinder housing being configured to conduct said exhaust gas throughsaid generally cylinder housing in a direction which is parallel to acentral axis of said generally cylinder housing and in contact with saidcatalyst coated material.
 5. The exhaust system of claim 4, wherein:said central axis is generally vertical.
 6. The exhaust system of claim1, wherein: an unobstructed path exists through said plenum to saidcatalyst module.
 7. The exhaust system of claim 1, wherein: theeffective cross sectional area of said plenum, at a plane midway betweensaid plurality of exhaust ports and said catalyst module and generallyperpendicular to the path of said exhaust gas, is greater than theeffective total cross sectional area of said plurality of exhaust ports.8. The exhaust system of claim 1, wherein: the effective cross sectionalarea of said plenum, at a plane midway between said plurality of exhaustports and said catalyst module and generally perpendicular to the pathof said exhaust gas, is greater than the effective total cross sectionalarea of said catalyst module.
 9. The exhaust system of claim 1, wherein:said plenum is configured to cause the velocity of said exhaust gas todecrease as it passes from said plurality of exhaust ports into saidplenum.
 10. The exhaust system of claim 1, wherein: said plenum isattachable to said marine engine.
 11. An exhaust system for a marineengine, comprising: a plurality of exhaust ports associated with aplurality of cylinders of said marine engine; a plurality of catalyzingelements disposed in fluid communication with said plurality of exhaustports, each of said plurality of catalyzing elements comprising catalystcoated material disposed within a generally cylinder housing, saidgenerally cylinder housing being configured to conduct said exhaust gasthrough said generally cylinder housing in a direction which is parallelto a central axis of said generally cylinder housing and in contact withsaid catalyst coated material; and a plenum disposed in fluidcommunication between said plurality of exhaust ports and said pluralityof catalyzing elements, wherein exhaust gas passing from said pluralityof exhaust ports to said plurality of catalyzing elements must passthrough said plenum, said plenum being attachable to said marine engineand configured to cause the velocity of said exhaust gas to decrease asit passes from said plurality of exhaust ports into said plenum, whereinthe effective cross sectional area of said plenum monotonicallydecreases from said plurality of exhaust ports to said plurality ofcatalyzing elements.
 12. The exhaust system of claim 11, wherein: saidplurality of catalyzing elements are disposed in parallel with eachother and in series with said plenum; said cross sectional areadecreases along the entire span of exhaust flow from said plurality ofexhaust ports to said plurality of catalyzing elements without changingto increasing values of said cross sectional area.
 13. The exhaustsystem of claim 12, wherein: said plurality of exhaust ports aredisposed in parallel with each other and in series with said plenum. 14.The exhaust system of claim 13, wherein: an unobstructed path existsthrough said plenum from any one of said plurality of exhaust ports toany one of said catalyzing elements.
 15. The exhaust system of claim 13,wherein: the effective cross sectional area of said plenum, at a planemidway between said plurality of exhaust ports and said plurality ofcatalyzing elements and generally perpendicular to the path of saidexhaust gas, is greater than the effective total cross sectional area ofsaid plurality of exhaust ports.
 16. The exhaust system of claim 13,wherein: the effective cross sectional area of said plenum, at a planemidway between said plurality of exhaust ports and said plurality ofcatalyzing elements and generally perpendicular to the path of saidexhaust gas, is greater than the effective total cross sectional area ofsaid plurality of catalyzing elements.
 17. The exhaust system of claim11, wherein: said central axis is generally vertical.
 18. An exhaustsystem for a marine engine, comprising: a plurality of exhaust portsassociated with a plurality of cylinders of said marine engine; aplurality of catalyst modules disposed in fluid communication with saidplurality of exhaust ports, each of said plurality of catalyst modulescomprising catalyst coated material disposed within a generally cylinderhousing, said generally cylinder housing being configured to conductsaid exhaust gas through said generally cylinder housing in a directionwhich is parallel to a central axis of said generally cylinder housingand in contact with said catalyst coated material; and a plenum disposedin fluid communication between said plurality of exhaust ports and saidplurality of catalyst modules, wherein exhaust gas passing from saidplurality of exhaust ports to said plurality of catalyst modules mustpass through said plenum, said plurality of catalyst modules beingdisposed in parallel with each other and in series with said plenum,said plurality of exhaust ports being disposed in parallel with eachother and in series with said plenum, said plenum being configured tocause the velocity of said exhaust gas to decrease as it passes fromsaid plurality of exhaust ports into said plenum, wherein the effectivecross sectional area of said plenum monotonically decreases from saidplurality of exhaust ports to said plurality of catalyst modules. 19.The exhaust system of claim 18, wherein: the effective cross sectionalarea of said plenum, at a plane midway between said plurality of exhaustports and said plurality of catalyst modules and generally perpendicularto the path of said exhaust gas, is greater than the effective totalcross sectional area of said plurality of exhaust ports; and theeffective cross sectional area of said plenum, at a plane midway betweensaid plurality of exhaust ports and said plurality of catalyst modulesand generally perpendicular to the path of said exhaust gas, is greaterthan the effective total cross sectional area of said plurality ofcatalyst modules; wherein said cross sectional area decreases along theentire span of exhaust flow from said plurality of exhaust ports to saidplurality of catalyst modules without changing to increasing values ofsaid cross sectional area.
 20. The exhaust system of claim 19, wherein:an unobstructed path exists through said plenum from any one of saidplurality of exhaust ports to any one of said catalyst modules, saidcentral axis being generally vertical, said plenum being attachable tosaid marine engine.